This invention relates to control of a valve open/close timing of an engine intake valve of a hybrid electric vehicle provided with an engine and an electric motor.
A hybrid electric vehicle which runs under the power of either an engine or motor, or both, is disclosed in pp. 39-52 of xe2x80x9cAutomobile Engineeringxe2x80x9d, Vol. 46, No.7, published in June, 1997 in Japan by Tetsudo Nihon Sha.
In a low vehicle speed region where the engine thermal efficiency is low, the vehicle runs mainly under the driving force of the motor, and when the vehicle speed and load are increased, the vehicle runs mainly under the driving force of the engine. Also, during deceleration, the motor functions as a generator due to the kinetic energy of the vehicle, generates power, and charges a battery.
When the vehicle is running in an urban area, it frequently starts and stops, and starting and stopping of the engine also occur frequently. Under such conditions, it is desirable to delay the valve closing timing of the intake valve to reduce friction of the engine. This is because reduction of engine friction leads to an increased regeneration power amount of the motor, improvement in the starting characteristics of the engine, and reduction of engine vibration, etc. For this reason, the hybrid electric vehicle varies the open/close timing of the intake valve of the engine according to the running conditions of the vehicle.
Regarding variation of the open/close timing of such an intake valve, Tokkai Hei 9-242520 published by the Japanese Patent Office in 1997 discloses a variable valve timing device wherein the initial rotation angle of an intake cam is varied.
In a hybrid electric vehicle, even in the low vehicle speed region where the vehicle moves only under the motor, it is necessary to restart the engine immediately and to increase engine torque quickly when the residual amount of power in the battery declines, or when a driver wants to perform rapid acceleration of the vehicle.
However, if the valve closing timing of the intake valve is retarded due to the aforesaid reason when the vehicle is running in an urban area, a delay occurs in the rise of engine output immediately after engine startup.
As a result, the output immediately after engine startup may be insufficient for the desired drivability of the vehicle.
It is therefore an object of this invention to satisfy the dual requirements of engine friction reduction and rapid rise of output during engine startup.
In order to achieve the above object, this invention provides a valve timing control device for changing over an open/close timing of an intake valve of an engine of a vehicle, wherein the engine comprises a combustion stop device for stopping combustion of the engine in a predetermined vehicle running condition. The control device comprises an actuator which varies the open/close timing of the intake valve according to an input signal, and a microprocessor programmed to determine whether or not engine combustion has stopped, and control the signal so that the open/close timing of the intake valve is retarded when engine combustion has stopped compared to a case when combustion has not stopped.
This invention also provides a valve timing control method for changing over an open/close timing of an intake valve of an engine of a vehicle, wherein the engine comprises a combustion stop device for stopping combustion of the engine in a predetermined vehicle running condition. The control method comprises determining whether or not engine combustion has stopped, and retarding the open/close timing of the intake valve when engine combustion has stopped compared to a case when combustion has not stopped.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.